T. Thangaradjou

In vitro antibacterial, cytotoxicity and haemolytic activities and phytochemical analysis of seagrasses from the Gulf of Mannar, South India.

It is essential to study the phytochemical constituents and toxicological properties of seagrasses when considering their food applications. Aqueous methanolic extracts of six seagrasses were evaluated for their antibacterial, cytotoxic (brine shrimp leathality assay) and haemolytic activity. Thin layer chromatography (TLC) and phytochemical analysis were used to compare the phytochemical profiles of six seagrasses. Among the six seagrasses examined, Halodule pinifolia and Cymodocea rotundata showed predominant growth inhibitory activity against all the tested human pathogens. Cytotoxicity of seagrass extracts against nauplii of Artemia salina revealed that Syringodium isoetifolium exhibited lesser toxicity with LC(50) value of 699.096 μg/ml. Of all the seagrasses tested, H. pinifolia recorded the minimum haemolytic activity of 2.07±0.63% at 1000 μg/ml concentration. Phytochemical analysis showed the presence of common plant chemical constituents which varied with respect to species. The present findings suggest the possible pharmacological applications of selected seagrasses that can be used as food ingredients.

Response surface methodology for the optimization of α-amylase production by Streptomyces sp. ML12 using agricultural byproducts

Amylases constitute one of the most important groups of enzymes for commercial use. In the present study, production of α-amylase was optimized using a newly isolated actinobacterial strain from the coral reef environment of the Gulf of Mannar Biosphere Reserve, India. It was identified as Streptomyces sp. ML12 based on chemotaxonomy, cultural and morphological characteristics, carbon source utilization and 16S rRNA gene sequencing. Fermentation variables were selected in accordance with the Plackett-Burman design and were optimized by response surface methodology. Five significant variables (rice bran and wheat bran — both agricultural byproducts, sodium chloride, magnesium sulphate and incubation period) were selected for the optimization via central composite design. The optimal features were rice bran (5.5 g/100 mL), wheat bran (5.3 g/100 mL), sodium chloride (2.8 g/100 mL), magnesium sulphate (1.4 g/100 mL) and 8 days of incubation period. Optimization of the medium with the above tested features increased the amylase yield by 4.4-fold.

Evidences for heavy metal contamination in surface sediments of seagrass ecosystem of Lakshadweep archipelago, India

Surface sediments of nine islands of Lakshadweep were evaluated for their heavy metal concentration (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn). Sediments of thirteen seagrass and seven non seagrass sites were collected randomly and analysed for heavy metal concentration using Inductively Coupled Plasma Optical Emission Spectrometer. Heavy metals like Cu, Ni and Zn were found in higher concentrations in the seagrass sediments, whereas other heavy metals such as Cd, Co, Cr, Fe, Mn and Pb were higher in non seagrass sediments. Different pollution indices were calculated to evaluate contamination level of all heavy metals in the sediments. Cadmium recorded higher contamination factor (1.733–21.067), enrichment factor (276.10–12,270) and Geo-accumulation Index (0.208–3.811) both in seagrass and nonseagrass sediments. Multivariate statistical analysis such as principal component analysis and cluster analysis coupled together with correlation co-efficient was used to identify the possible sources of heavy metal pollution in the region. Average concentrations of Cd in Lakshadweep islands were slightly higher than effective range, low but still below effective range medium. All other metals were still below these ranges indicating fairly uncontaminated sediment in the region.

Differential methods of localisation of fungal endophytes in the seagrasses

ABSTRACT Sections of three seagrass species (Halophila ovalis, Cymodocea serrulata and Halodule pinifolia) were assessed for endophytes based on differential staining using light and fluorescence microscopy method. Acridine orange and aniline blue detected endophytic fungi in 20% and 10% of the segments, respectively, whereas lactophenol cotton blue was more sensitive to detect the fungal hyphae in 70% of the segments. Hyphae were the principal fungal structures generally observed under the cuticle, within the epidermal cells, mesophyll (Parenchyma) cells and occasionally within the vascular tissue that varied in type, size and location within the leaf tissue. Present study also recorded the sporulation for the first time from the seagrass endophytes. Successfully amplified products of the ITS region of endophytic fungal DNA, directly from seagrass tissue and also from culture-dependent fungal DNA clearly depicted the presence of endophytic fungi in H. ovalis with two banding patterns (903 and 1381 bp) confirming the presence of two dominant fungal genera. The fingerprinting of endophytic fungal community within the seagrass tissue was assessed using denaturing gradient gel electrophoresis (DGGE) that derived with multiple bands that clarified the presence of more than one taxon within the seagrass tissue.

Inter-annual and seasonal variations in hydrological parameters and its implications on chlorophyll a distribution along the southwest coast of Bay of Bengal

Seasonal and inter-annual variability of hydrological parameters and its impact on chlorophyll distribution was studied from January 2009 to December 2011 at four coastal stations along the southwest Bay of Bengal. Statistical analysis (principal component analysis (PCA), two-way analysis of variance (ANOVA) and correlation analysis) showed the significant impact of hydrological parameters on chlorophyll distribution in the study area. The ranges of different parameters recorded were 23.8–33.8°C (SST), 4.00–36.00 (salinity), 7.0–9.2 (pH), 4.41–8.32 mg/L (dissolved oxygen), 0.04–2.45 μmol/L (nitrite), 0.33–16.10 μmol/L (nitrate), 0.02–2.51 μmol/L (ammonia), 0.04–3.32 μmol/L (inorganic phosphate), 10.09–85.28 μmol/L (reactive silicate) and 0.04–13.8 μg/L (chlorophyll). PCA analysis carried out for different seasons found variations in the relationship between physico-chemical parameters and chlorophyll in which nitrate and chlorophyll were positively loaded at PC1 (principal component 1) during spring inter-monsoon and at PC2 (principal component 2) during other seasons. Likewise correlation analysis also showed significant positive relationship between chlorophyll and nutrients especially with nitrate (r=0.734). Distribution of hydrobiological parameters between stations and distances was significantly varying as evidenced from the ANOVA results. The study found that the spatial and temporal distribution of chlorophyll was highly dependent on the availability of nutrients especially, nitrate in the southwest Bay of Bengal coastal waters.

Trend in coral-algal phase shift in the Mandapam group of islands, Gulf of Mannar Marine Biosphere Reserve, India

The present study revealed proliferation of macro-algae modifying coral reef ecosystems in a different manner due to diseases and sedimentations in the Mandapam group of islands in the Gulf of Mannar. Benthic surveys were conducted with major attack of seven coral reefs diseases with high sedimentation rate, nine species of fleshy macro-algae (Turbinaria ornata, Turbinaria conaides, Caulerpa scalpelliformis, Caulerpa racemosa, Kappaphycus alvarezii, Padina gymnosphora, Sargassum wightii, Ulva reticulata and Calurpa lentillifera) proliferation against major corals life forms (Acropora branching, Acropora digitate, Acropora tabulate, coral massive, coral submassive, coral foliose and coral encrusting). The results confirm that diseased corals most favor to macro-algae growth (15.27%) rather than the sedimentation covered corals (8.24 %). In the degradation of coral life forms, massive corals were more highly damaged (7.05%) than any other forms. Within a short period of time (May to September), coral coverage shrank to 17.4% from 21.9%, macro-algae increased 23.51% and the average sedimentation rate attained 77.52 mg cm−2d−1 with persisting coral reef diseases of 17.59%. The Pearson correlation showed that the coral cover decreased with increasing macro-algae growth, which was statistically significant (r = −0.774, n = 100, P < 0.0005). The proliferation of the various macro-algae C. scalpellifrmis, T. ornata, C. racemosa, T. conaides, U. reticulata, S. wightii, K. alvarezii, P. gymnosphora and C. lentillifera increased with percentages of 6.0, 5.8, 5.7, 4.9, 4.2, 3.7, 2.7 and 1.9, respectively. If this trend continues, the next generation of new recruit corals will undoubtedly lead to a phase shift in Gulf of Mannar corals.

Biogeochemical processes in tropical seagrass beds and their role in determining the productivity of the meadows

Porewater nutrient profiles such as nitrate (0.33–1.38 μM), ortho phosphate (1.47–3.44 μM), total nitrogen (1.24–7.22 μM) and total phosphorus (3.51–5.98 μM) in seagrass ecosystem subjected to different nutrient loading indicated the limitation of porewater nutrients in all the strata of different sampling sites of Palk Bay region. Sediment pH in the seagrass beds were alkaline and anoxic condition increased with increase in depth (56.2 mV to −52.7 mV). Significant positive correlation was observed between silt content and carbon (r = 0.359, P < 0.05) and nitrogen contents (r = 0.381, P < 0.05) of the sediment. Specieswise interpretation also indicated C/N ratio of the stations greatly promoted the biomass in Halodule pinifolia and Cymodocea serrulata. The sediment C/N stoichiometry (4.7: 1–16: 1) indicated that autochthonous C sources regulates the C biogeochemical processes in seagrass ecosystem which is well corroborated by the least square regression value (R2 = 0.92) obtained between the C/N ratio and biomass. Meanwhile, the N/P ratio (11.7: 1–17.2: 1) indicated P deficiency in the seagrass beds. Though, nitrogen limitation was evident in the porewater, but it has not reflected on seagrass biomass and productivity which is, evidenced by the higher biomass of individual species. Nutrient biogeochemical transformations across the sediment-water interface influence the productivity of seagrasses in the Palk Bay region. In addition, nutrient pollution, eutrophication and light limitation due to algal mats decreased the growth of seagrasses which need to be attempted to develop the nutrient policies for sustainable management and restoration of seagrass ecosystem.

Hydrographic and sediment characteristics of seagrass meadows of the Gulf of Mannar Marine Biosphere Reserve, South India

The aim of the study was to examine the spatial and temporal variations in the physicochemical parameters of seagrass meadows of the Gulf of Mannar, South India using multivariate statistical techniques, namely, cluster analysis (CA) and principal component analysis (PCA), to explore the relationship. There were clear spatial and temporal variations in physicochemical variables of the seagrass meadow of the Gulf of Mannar, but such changes were subjected to seasonal variations especially during monsoon and post-monsoon seasons. The multivariate statistical techniques, viz., CA and PCA helped in the discrimination of islands according to the physicochemical parameters of the seagrass meadows. It was inferred that electrical conductivity, nitrate, particulate organic carbon, and phosphate strongly determined the discrimination of 19 islands, respectively, upon physicochemical characteristics of their seagrass meadows. These results highlight the important role of seagrasses in the Gulf of Mannar Marine Biosphere Reserve.